Question 435822
Whoops, wasn't thinking properly. The other tutor stated 9 cannot be a possible side length for a triangle. This is correct, but for a completely different reason.


Suppose a,b,c are the lengths of the triangle with {{{a <= b <= c}}}, and {{{a+b+c = 18}}}. By the triangle inequality, {{{a+b > c}}}. Adding c to both sides, {{{a+b+c > 2c}}}. Since a+b+c = 18, {{{18 > 2c}}}, {{{9 > c}}}, hence c must be less than 9, so 9 cannot be a side length.